Vascular tissue

“ It is composed of fibrous tissue mixed with elastic fibers.
"Followed toward the capillaries, the coats of the artery gradually diminish in thickness, the endothelium resting directly upon the internal elastic membrane so long as the latter persists, and afterward on the rapidly attenuating media. The elastica becomes progressively reduced until it entirely disappears from the middle coat, which then becomes a purely muscular tunic, and, before the capillary is reached, is reduced to a single layer of muscle cells. ”

“ The predominance of elastic tissue permits of great distention by the blood forced into the artery at every heartbeat, the caliber of the tube being less markedly under the control of the vasomotor nerves than is the case in the small arteries, where the muscle tissue is relatively more developed. The adventitia of the large arteries is strong and firm, and is made up of interlacing fibroelastic tissue, of which some of the bundles are arranged longitudinally. ”

“ Every artery divides and subdivides as it passes outward from the great central artery of the body—the aorta—so that the vascular system may be likened to a tree, with trunk, boughs, branches, and twigs. Each terminal division of an artery supplies with blood a little cone-shaped mass of brain, the base of the cone being the gray surface of the brain, and its apex being the point of entrance of the little artery. ”

“ In this manner a vascular circle, the circle of Willis, is formed, which permits of freedom of the arterial circulation by the anastomoses between arteries not only on the same side, but on opposite sides of the mesial plane. The vertebral and internal carotid arteries, which are the arteries of supply for the brain, are distinguished by lying at some depth from the surface in their course to the organ, by having curves or twists in their course, and by the absence of large collateral branches. ”

“ It rises up rapidly, new systems of blood-vessels forming in it, till its height is twice its diameter; then an osseous deposit is commenced at the circumference of the top of the pedicel. As this deposit rises it thickens very slowly, the upper extremity presenting a thin, serrated edge. Blood-vessels from the periosteum traverse this tissue, supplying it with nourishment. This is the source of supply from without; but there are internal sources also, viz., arteries passing up through the pedicel, and answering to the medullary arteries of long bones. ”

“ Their diameter is so small that the red corpuscles have to pass in single file and may even then be squeezed out of shape. As they have no muscular tissue in their walls, they have no power of contracting. Their walls, however, like those of the smaller arteries and veins, are porous and by virtue of this quality they play an important part in the economy, since in them the exchange takes place between the tissues and the blood.
The arteries in general carry freshly oxidized blood and the veins blood from which the oxygen has been largely used up and which contains waste material. ”

“ The large arteries differ from those of medium size mainly in the fact that there is no sharp line of demarcation between the intima and the media. There is also much more elastic tissue distributed in firm bundles throughout the media, and there are fewer muscle fibers, giving a more compact appearance to the artery as seen in cross section. ”

“ In the first part of the aorta, pulmonary artery and arteries of the retina there is no muscular coat. Internal to the muscular coat is the elastic fenestrated coat, formed of a smooth elastic membrane perforated by small apertures. Most internal of all is a layer of endothelial cells, which form the free surface over which the blood flows. The arteries are not nourished by the blood which flows through them, but by minute vessels, vasa vasorum, distributed in their external, elastic and muscular coats. ”

“ A cupped state of the blood most commonly occurs in association with inflammation of the serous membranes and parenchymatous organs, and may generally be regarded as evincive of a high degree of vascular excitement. ”

“ The vascular system itself is quite peculiar, consisting of lacunae and channels destitute of endothelium, situated within the thickness of the basement-membrane of the body-wall, of the gut-wall and of the mesenteries. The blood, which is a non-corpuscular fluid, is propelled forwards by the contractile dorsal vessel and collected into the central blood-sinus; this lies over the stomochord, and is surrounded on three sides by a closed vesicle, with contractile walls, called the pericardium (Herzblase) . ”

“ In the aorta and large branches there is much elastic tissue and relatively little muscle. When the vessels have reached the organs, they are found to be structurally changed in that there is in them a relatively small amount of elastic tissue but a great deal of smooth muscle. ”

“ Although in most instances the organs of the body are supplied with arterialised blood conveyed to them by arteries, there are nevertheless cases in which an organ may receive venous blood by a vein in addition to arterial blood supplied by an artery. For example, the capillaries of the liver not only receive blood from the hepatic artery, but also venous blood by a large vein (hepatic portal vein) , formed by the union of a number of smaller veins by which venous blood is collected from the capillaries of the stomach, intestine, spleen, and pancreas. ”

“ Examine these surfaces in chronic and acute inflammations, of which they are the seat, in the first especially, they exhibit a vascular net-work, so full of blood, that their redness is often deeper than that of the muscles.
All the organs of which I have spoken above, exhibit the same phenomenon. Observe what takes place in the skin; fine injections show there infinitely more vessels than are filled with blood in a natural state; the face of a child well injected, is wholly black. ”

“ They may often be seen in sections, and are lined with nucleated cells, similar to those of the glands. These are surrounded by coatings of unstriped muscular fibre, running both around and lengthways, and also by connective-tissue fibres. In the arteries, the muscular coating is much stronger than in the veins. ”

“ In every chair of anatomy and physiology (which studies were not then separated) in Europe, it was taught that the blood brought to the liver by the portal vein, and carried out of the liver to the 'vena cava' by the hepatic vein, is distributed from the right side of the heart, through the other veins, to all parts of the body; that the blood of the arteries takes a like course from the heart towards the periphery; and that it is there, by means of the 'anastomoses', more or less mixed up with the venous blood. ”

“ Nothing is more simple, as you perceive, than to distinguish an artery from a vein; you have only to ascertain what is inside of it. When the blood goes out to our organs to nourish them, it is arterial; when it is returning back after having nourished them, it has become venous. But what—you will ask—is it going to do now at the heart, towards which it is on its road? It is going to seek there a fresh impetus which shall send it once more into the lungs, where it will again become arterial, i. e. and once more capable of affording nourishment to the organs. ”

“ If the ligature be too tight, the blood will not flow through the opening in the vein. The reason of this, is, that the artery is compressed, in this case, as well as the vein; and as the veins derive their blood from the arteries, it follows that if the blood's motion be obstructed in the latter, none can flow from them into the former: when we wish to open an artery, the orifice must be made above the ligature. ”

“ When the main artery of a limb has been obstructed, or tied by the surgeon's ligature, we find the nutrition of the tissues beyond is supported by the blood finding its way through the smaller anastomosing arteries, and in time we observe these smaller arterial branches to become considerably enlarged, thus adapting themselves to the increased amount of blood they have been called upon to transmit. ”

“ The tissue with which they are continuous, which is exactly equivalent to the tissue from which the neural arches originate, is not truly a part of the rib. In the tail, behind the anus and kidneys, the cardinal veins fuse to form an unpaired caudal vein below the aorta, and in this part a fresh series of processes originates on each side from the hæmal tissue adjoining the cartilaginous sheath of the notochord, and eventually, by the junction of the processes of the two sides, a canal which contains the aorta and caudal vein is formed below the notochord. ”

“ The muscular coats of the arterial system are then brought into action by the stimulus of distention, and propel the blood to the mouths, or through the convolutions, which precede the secretory apertures of the various glands and capillaries.
In the vessels of the liver there is no intervention of the heart; but the vena portarum, which does the office of an artery, is distended by the blood poured into it from the mesenteric veins, and is by this distention stimulated to contract itself, and propel the blood to the mouths of the numerous glands, which compose that viscus. ”

“ Associated with vascular dilatation there is extensive leucocyte extravasation into the perivascular spaces, the course of the line of the attack being mapped out by white and yellow lines and areas of exudation. ”

“ A sufficiency of blood to distend it collects within the venous cistern. The arterial system, owin to its elasticity and contractility, empties. If the heart now begin to beat, blood is taken from the venous system and is driven into the arterial system., The arteries receive more blood than can escape through the capillary vessels, and the arterial side of the system becomes distended, until equilibrium is reached, and as much blood escapes into the venous side per unit of time as is delivered by the heart. ”

“ Whenever, on incising an artery, you find blood in the artery, and it runs freely, it indicates that there is a considerable quantity of blood in the arterial system. This blood then should be removed, because, were fluid to be injected into the artery, when it is full of blood and in this congested condition, all of this blood would be pushed ahead of the fluid toward the center of pressure, and from there large quantities would be pushed back into the tissues of the face, which would result in a greatly discolored face and a very poor cosmetic effect. ”

“ A great vein extends forwards along the caudal region below the notochord, and exhibits contractility in a forward direction; it is bent anteriorly, passing into another tube-like pulsatile trunk, the branchial heart, which runs along the middle of the base of the pharynx, sending off branches on each side to the branchiæ; each of these branches has a small contractile dilatation (bulbillus) at its base. The two anterior branches pass directly into the aorta, the others are branchial arteries, the blood of which returns by branchial veins emptying into the aorta. ”